altapowder

1st, thanks for all the help from everyone on this forum. my story & findings.
my 05 s55amg @17k miles, had TPMS sensors dropping out with the new year. LR 1st, then a 2nd then NO pressures displayed. as each individual wheel TPMS(ensor) failed I got 'dashes' where previous individual pressure indications were displayed.

OK - homework here educated me that they have a 5 to 7 year life span and replacement is the fix - do the set. price shock from local dealer (to the North) resulted in more homework and I found 315mhz sensors for $140 (NAPA pn/92-1134) made by BERU AG, which is the only sensor for this car. prices varied by as much as double, well more, at the MB dealer. I'll buy sensors & find a tire store that has experience with the delicate sensor install. the NAPA valve stem KIT for this car does not fit the (correct) sensor. alrighty then - the Mercedes Valve Stem KIT (MB p/n A 001 401 61 13) is available for $20. I get 4. Back to Firestone for the install.

NEW sensors do not bring system back into operation. the individual ID Numbers on each sensor (as read from the part itself - before install - or with a scanner such as the one SnapOn makes) need to be entered into the vehicle software. off we go the the 2nd MB Dealer (to the South - a much better experience) to "enter" the sensors into the vehicle. system does not come to life and a CODE presents itself indicating "LR, indicating Left Rear Sensor inop with a statement that one, or more sensors are inoperative. :

I AM having fun now. Firestone gets a replacement sensor and on close visual (magnified 10x) examination the removed/new sensor has a hairline crack.
seems the 4NM torque spec has reason behind it ! with the 2nd NEW (Left Rear) sensor installed back to the Dealer to enter some more sensor ID Numbers. another 40 minute session and my System comes to life but only for a few miles . . . . jeeeeze, I say - or something like that !

I get home and read a bit here on this forum and come across information
supporting the concept that the TPMS "system", looking to handshake with REPLACEMENT Sensors is very sensitive to the SPECIFIED TIRE PRESSURES
as indicated on the door jamb. the Firestone tech set pressures roughly 10% higher than what is specified.

I reduced tire pressures to comply with what is SPECIFIED, using a accurate gauge & cross checked by another, and without delay the System came to life with indications on the TPMS System indicating the measured tire pressures.

my conclusion . . . . the TPMS 'system' looks to find a 'specified' pressure
to handshake & confirm proper operation (and perhaps accuracy ?) of new/replacement TPMS sensors. now that my system is in operation I have increased, and decreased pressure by 5 lbs. to confirm system operation and it works as advertised. accurate too !

SPECIFIED Torques, on the Valve Stems & the individual TPMS Sensor are,
- SPECIFIED - for a reason. the installer needs to have & use a 1/4 inch drive torque wrench. I suspect my 'bad' NEW sensor failed due to over torquing
during the 1st install.

NAPA p/n 92-1134 31mhz Sensors, by BERU AG fit this application
NAPA Valve Stem Kits, specified for this car DO NOT fit the Sensor (hmmm !)
MB Valve Stem KIT (p/n A 001 401 61 13), $20/ea DO FIT the Sensor

and now, I'm good for another handful of years & more ed-u-MA-kay-shun
is under my belt. I hope this helps some other folks.

thanks to all here for the clues to resolving this . . . problem.

until then, d